Objectives: (1) Restore belief in the external world
(2) Revisit the problem of error
(3) Prove that my (i.e., Descartes') essence is thinking
(4) Provide a criterion to tell dreaming from waking

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(1) Restoring Belief in the External World

A 'Probable' Argument for Believing in the External World:Distinguishing between the intellect and the imagination: "the
mind, when it understands, in a sense turns toward itself and looks at
one of the ideas that are in it, whereas when it imagines, it turns towards
the body, and intuits in the body something that conforms to the idea"
(93)
Imagination requires a body, the intellect does not.
How does imagination require a body?"When external objects act on my senses, they print on them an idea,
or rather a figure of themselves. And when the mind attends to these images
imprinted on the [pineal] gland in this way it is said to have sense-perception.
When, on the other hand, the images on the gland are imprinted not by external
objects, but by the mind itself … then we have imagination." (AT
V 162-3, from the Conversation with Burman)

The imagination uses the pineal gland as a sort of scratch pad.

How does this lead to a probable argument that the external world exists?

"I easily understand that the imagination can be actualized in this
way, provided a body does exist. And since I can think of no other way
of explaining imagination that is equally appropriate, I make a probable
conjecture from this that a body exists."

But "this is only a probability." (93)

Can we do better than this?

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A 'Certain' ArgumentEssentially Descartes argues that, given that we know, God is not a
deceiver and that we cannot help but believe in an external world, there
really must be an external world.

A more careful summary of the argument:

(1) I have in me "a faculty for receiving and knowing the ideas of sensible
things". (96-7)
(2) These ideas must come from someplace, i.e., there must exist "either
in me or in something else, a certain active faculty of producing or bringing
about these ideas." (97)

(3) "this faculty surely cannot be in me, since it clearly presupposes
no act of understanding, and these ideas are produced without my cooperation
and often even against my will." (97)

Remember Descartes' theory of the transparency of the mind here
(see notes on Meditation III).
If you were producing these ideas yourself, you'd know about it.
(4) So, if I don't produce my ideas of sensible things myself, these ideas
must be produced by the sensible things themselves or else by "God, or
some other creature more noble than a body, which contains eminently all
that is contained objectively in the ideas." (97)
See the notes on Meditation
III for the idea of eminent containment.

(5) But I can't tell which of the possibilities mentioned in #4
holds.

(6) Now, "since God has given me no faculty whatsoever for making this
determination, but instead has given me a great inclination to believe
that these ideas issue from corporeal things, I fail to see how God could
be understood not to be a deceiver, if these ideas were to issue from a
source other than corporeal things. And consequently corporeal things exist."
(97)

Is this argument convincing?
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An Addendum to the Argument -- What is the external world like?"perhaps not all bodies exist exactly as I grasp them by sense … But
at least they do contain everything I clearly and distinctly understand"
(97)
"although I feel heat as I draw closer to the fire, and I also feel pain
upon drawing too close to it, there is not a single argument that persuades
that there is something in the fire similar to that heat, any more than
to that pain. On the contrary, I am convinced only that there is something
in the fire that … causes in us those sensations" (99)

The limitations of the proof of the external world: How well
Descartes' argument for the existence of the external world works depends
on what sort of property we're dealing with.

"perhaps not all bodies exist exactly as I grasp them by sense … But at
least they do contain everything I clearly and distinctly understand" (97)
"As far as the remaining matters are concerned, which are either merely
particular (for example, that the sun is of such and such a size or shape,
and so on) or less clearly understood (for example, light, sound, pain
and the like), … these matters are very doubtful and uncertain" (97)

But There's a Reason for Optimism:

"surely there is no doubt that all that I am taught by nature has
some truth to it; for by 'nature,' … I understand nothing other than God
himself or the ordered network of created things which was instituted by
God." (97)

"There is nothing that this nature teaches me more explicitly than that
I have a body that is ill-disposed when I feel pain, that needs food and
drink when I suffer hunger or thirst, and the like. Therefore, I should
not doubt that there is some truth in this." (97) [Note: 'some truth']

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(2) A New Problem of Error

But sometimes nature does steer me wrong:
When I have dropsy, I am thirsty although I shouldn't drink.

When I have phantom limb pain, I feel pain in limbs that are no longer
there.

The Solution: This is an unavoidable 'design flaw' in humans. Sense
perception happens by means of nerves 'pulling' on the pineal gland which
somehow contacts the soul. This makes it possible for some 'pulls' to be
misleading.How Mind and Body Interact: "my mind is not immediately affected
by all the parts of the body, but only by the brain, or perhaps even by
just one small part of the brain [i.e., the pineal gland]" (101)
The pineal gland is the 'go between' for mind and body.

The Design Flaw: "the nature of the body is such that whenever
any of its parts can be moved by another part some distance away, it can
also be moved in the same manner by any of the parts that lie between them"
(101)

But this doesn't reflect badly on God: "I can think of no better
arrangement than that it produces the one sensation that, of all the ones
it is able to produce, is most especially and most often conducive to the
maintenance of a healthy man. … nothing else would have served so well
the maintenance of the body"

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(3) Proving Mind and Body are Distinct

There are actually two arguments for this point.

(i) "all the things that I clearly and distinctly understand can be
made by God such as I understand them. For this reason my ability clearly
and distinctly to understand one thing without another suffices to make
me certain that the one thing is different from the other, since they can
be separated from one another, at least by God."
If two things are logically distinct, they are actually distinct?

In the Second Meditation, I judged that "nothing else belongs to my
nature or essence except that I am a thinking thing, [therefore] I rightly
conclude that my essence consists entirely in my being a thinking thing."
(96)

Is this convincing?(ii) "there is a great difference between a mind and a body in that
a body, by its very nature, is always divisible. On the other hand, the
mind is utterly indivisible. For when I consider the mind, … I cannot distinguish
any parts within me; rather, I understand myself to be manifestly one complete
thing." (100-1)
What about the will and the understanding?
These cannot "be called 'parts' of the mind, since it is one and the same
mind that wills, senses and understands." (101)
"This consideration alone would suffice to teach me that the mind is wholly
diverse from the body, had I not yet known it well enough in any other
way." (101)
Why bring up this additional proof?
Because of the payoff, if the soul is indivisible then presumably it's
indestructible (since it can't be broken down). Think of Plato.
*****************

(4) Telling Dream from Reality

"the hyperbolic doubts of the last few days ought to be rejected as
ludicrous." With regard to dream and reality, "I now notice there is a
considerable difference between these two; dreams are never joined by the
memory with all the other actions of life, as is the case with those actions
that occur when one is awake." (103)
Is this persuasive if we make the assumption that God exists and is
not a deceiver?
What if we don't make those assumptions?[Philosophy 1200]